The declaration was made because 42 days have passed since the last person confirmed to have Ebola tested negative for the second time, a WHO statement said.

But the county now enters a 90-day period of heightened surveillance to make sure that any new cases are identified quickly, the WHO said.

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WHO: Government has 'shown extraordinary leadership'

The statement included praise for the government of Guinea and its people, which the WHO said had "shown extraordinary leadership in fighting the epidemic."

However, the global health organization said that challenges remain -- among them, that the virus may persist in the semen of some survivors for up to a year.

The disease is passed through direct contact with the bodily fluids of an infected person.

"The coming months will be absolutely critical," said Dr. Bruce Aylward, the head of Ebola response for the WHO.

Patient zero: A 2-year-old boy

Researchers from The New England Journal of Medicine say they think the first person to become infected with the disease was Emile Ouamouno, a 2-year-old boy who lived in Gueckedou, a town in southern Guinea.

The total number of people infected with Ebola eventually totaled more than 28,000, according to the World Health Organization. And the number of people who died from the disease reached more than 11,200.